Chapter 3 Peak Detection and Labeling
3.2.5Charge State
Determination and Examples
NOTE:
This section includes:
•Charge state determination
•Charge state parameter examples
•Charge state determination troubleshooting
For information on isotopes, see Appendix B, Overview of Isotopes.
Charge state is determined by evaluating the relative isotope peak spacing. The expected peak spacing is determined by the Max Charge State, plus or minus a tolerance value. The tolerance is calculated as (proton mass/charge state) × 15%, where proton mass equals 1.007276456.
During charge state determination, the software starts with the most intense peak and the peak spacing determined by the Max Charge state, then evaluates all detected peaks. The software iteratively decreases the Max Charge State and repeats the process for all peaks not already identified as members of an isotope cluster.
To accurately determine charge state, Charge State parameters must be set appropriately. The following sections illustrate:
•Max Charge State and Max Isotope # set correctly
•Max Charge State set too low
•Max Isotope # set too low
•Effect of Minimum Intensity